Connector with bonded insulating sleeve and method of making same



Oct. 7, 1958 T c. FREEDOM 2,855,581

CONNECTOR WITM BONDED INSULATING SLEEVE AND METHOD OF' MAKING SAME Filed March` 26. 1954 TEL- 1.4.

,ATTORN S.'

United States Patent O ECt'tlslNECTIR WITH BONDED INSULATING SLEEVE AND METHOD F MAKING SAME Thomas C. Freedom, Dillsburg, Pa., assignor to Aircraft- Marine Products, Harrisburg, Pa.

Application Marcil 26, 1954, Serial No. 418,919 4 Claims. (Cl. 339-218) This invention relates to insulated electrical connectors of the type that are adapted to be crimped onto electrical conductors. More particularly, this invention relates to an improved method of bonding rigid-plastic insulating jackets to a metal fermle or liner in such a connector to provide a novel insulated electrical connector having superior characteristics.

Metallic connectors that are adapted to be crimped i. e., pressure formed, rapidly and simply onto one or more electrical conductors, as by means of a hand or power crimping tool, have found widespread use. Such a connector, whether formed from extruded tube or by drawing a seamless ferrule from an initially at strip Aof copper or other malleable metal, by assembly of Stampings or by stamping out a flat blank and rolling at least a part thereof into tubular shape with or without -brazing or other reinforcement of its seam, Vis advantageously provided with rigid-plastic insulation, i. e., a layer of insulating plastic so tough that the insulated fermle can be crimped under heavy pressure onto one or more bare conductors. This has been broadly disclosed and claimed in the Patent of Watts 2,410,321 and of Swengel 2,654,873.

During the crimping operation, severe stresses are typically applied to both the ferrule and the conductor, resulting in plastic flow, and cold-forging them together into an excellent electrical connection of stable, low contact resistance. lt has been found desirable as set forth in the patent of Buchanan 2,379,567, and in the said Swengel patent, to position a close-fitting thin seamless sleeve, such as one formed of copper, brass or bronze, around the ferrule body prior to the crimping operation, this sleeve having the insulation cemented to it. Nylon, which is extensively used for this purpose, displays extraordinary resistance to solvents and relatively high temperatures, but has proven diiicult t'o bond to the metal ferrule without impairing its properties for crimping and use under some conditions.

Accordingly, it is an object of the present invention to provide an improved insulated electrical connector. More specifically it is an object to bond nylon on the ferrule portion of a connector without impairment of its properties. It is another object of this invention to provide a more satisfactory method of insulating an electrical connector, whereby the resulting insulated connector may be crimped onto a wire without destroying its insulation, and which provides for simplicity and economy in the required manufacturing operations. Other objects and advantages will be pointed tout in, or apparent from, the following description considered together with the accompanying drawings in which:

Figure l is a perspective View of one type of connector embodying the invention;

Figure 2 is a cross-section view along plane 2-2 of the connector ferrule of Figure l Figure 3 is a cross-section view along a longitudinal plane through the connector ferrule of Figure l;

`Figure 4 is a iiow diagram in block form outlining the CTI Patented Oct. 7, 1958 process steps in the manufacture of a connector according Ito the present invention;

Figure 5 is a schematic diagram of a resistance heating arrangement;

Figure 6 shows a sleeve assembly positioned over a heating mandrel; and

Figure 7 shows a magnetic induction heating coil arrangement.

One f-orm of an insulated connector adapted for crimp- `ing onto one or more wires or other electrical conductors is shown in Figure l. This connector includes a ring tongue 10 for attachment to a binding post, etc., and a composite, laminated ferrule generally indicated at 12 into which the conductors are to be inserted prior to the crimping operation.

This ferrule 12 includes an interior metallic portion 14, serving as the w-ire barrel, and which is typically formed of copper, aluminium, iron or one of their alloys and integral with the tongue 10. Surrounding, and secured to the interior barrel portion 14, is a metal sleeve 16, typically formed of copper, brass, bronze, nickel, aluminum, etc. which may serve among others the functions set forth in the Buchanan Patent No. 2,379,567. The exterior of the -ferrule 12 comprises a plastic jacket 18 adhesively secured to the sleeve 16 and thus insulating it against short-circuit contacts. This jacket is advantageously formed of nylon but in the broader aspect of the invention may be of vinyl chloride slightly plasticized e. g., with a 2-5% vinyl acetate copolymerized therewith and/ or a small percentage of external plasticizer. In general, this plastic is a rigid, tough, very high tensile strength and high melting point plastic, chemically stable and resistant to solvents.

Figures 2 and 3 show this connector in cross-section taken along planes 2 2 and 3 3, respectively, of Figure l. These views show a seamless plastic jacket 18 disposed around and covering a seamlessmetal sleeve 16, which in turn is positioned aroundl the interior wire barrel 14.

vIf the sleeve 16 is to be omitted and the jacket applied directly to the barrel 14 the. latter may with advantage have `a brazed seam 20 (see Figure 2), which runs the length of the interior barrel portion 14; and this may be used even where the sleeve 16 is included in the ferrule.

For the purposes of fully illustrating the invention and to point out the nature .and principles thereof, certain specific examples of preferred structures and manufacturing processes are described herein and various alternatives suggested. These examples, of course, are not to be taken as exhaustive and limiting the scope of the invention, but rather are to be considered as 4an aid to others skilled in the art so that they may be able to adapt the invention to such forms as may be ybest suited for a particular application.

Referring now to Figure 4, which is a block diagram of a manufacturing process rfor producing a nylon insulated connector, a thin seamless drawn copper sleeve is first cleaned and thoroughly dried (step 1). The cleaning operation may, for example, consist of etching the sleeve surfaces with nitric or sulphuric acid, or electro-polishing the surfaces by reverse plating in a phosphoric acid bath. A nitric acidv bath has been found to give superior results in many cases, since it not only leaves a substantially clean surface free from harmful impurities, but also tends somewhat to roughen the copper surface in a manner advantageous for the further processing to be described below. After the cleaningl operation, the sleeve was thoroughly dried, for example by exposing it to a stream of dry air.

Reverting to Figure 3, this sleeve 16 is advantageously made with a circumferential indent at 17 which serves both to guide the wire into the barrel 14 and to secure the sleeve against axial rem-oval. The length of the sleeve is such that the opposite end extends beyond the corresponding end of the barrel 14, so that it can be deformed inwardly to secure the other end of the sleeve.

A rigid nylon tube or jacket, for example formed of FM3003 Dupont nylon and preformed as extruded tubing, was then forced onto the copper sleeve or injection molded thereon (step 2). The inner diameter of the nylon jacket should be slightly smaller than the outer diameter of the copper sleeve, to give a tight fit between the two. This assures that the sleeve and insulating jacket do not slide apart during the subsequent operations, and also improves the eventual bond achieved between the two materials.

Although not essential to the formation of a satisfactory nylon-copper bond, it has been found advantageous, prior to assembling the nylon jacket and copper sleeve together, to coat the outer sleeve surfaces with a relatively thin film of cement chosen to have the best possible adhesion to the metal and to give the best possible base for adhesion by melted nylon. The preferred adhesive for this purpose is a partially polymerized resorcino1-formaldehyde condensation resin dissolved in aqueous alcohol. This phenolic lacquer is advantageously applied in such a manner that, after approximately l milligram per square centimeter remains on the outer surface of the sleeve. After application of the adhesive, excess lacquer may be removed by centrifuging, and the coated sleeve advantageously is air-dried and/or baked, e. g. by placing it in an oven at 320 F. for a period of about minutes, in order to completely dry and partly cure the resin. When an adhesive coating is used, special care must be taken in selecting the nylon jacket inner diameter to assure that it gives a tight fit but does not remove the adhesive resin layer when it is forced over the sleeve.

With the nylon jacket securely in place on the copper sleeve, heat is then applied (step 3) directly at the interface with the copper wall of the sleeve. This heat is advantageously applied suddenly, and for only a short period of time (e. g. for less than a minute), and should be suiciently intense to momentarily raise the tempera ture of the copper above the melting point of the nylon (e. g., to about 500 F.). The duration and intensity of the applied heat is adjusted so that the heat transfer to the nylon raises the temperature of the nylon, to a very shallow depth immediately adjacent the copper sleeve (i. e. the first thousandth of an inch or so radially), just barely above its melting point, and thereby effects fusion of the nylon and wetting of and adhesion to the copper. Immediately after this inner layer of the nylon begins to melt, the heating is stopped and, if the thermal drying, a coating of i capacity of the heated parts is such as to continue fusion,

the assembly is chilled (step 4) for example by a cold water bath. Thus the fused inner layer of the nylon is promptly solidified and creates a bond with the outer surface of the copper sleeve. It has been found advantageous to use nylon jackets slightly thicker (e. g. several thousandths of an inch) than would theoretically be rcquired for the required voltage breakdown strength.

Various means may be employed for applying intense p heat suddenly to the copper sleeve. For example, as shown schematically in Figure 5, the sleeve assembly generally indicated at 28, and which includes a copper sleeve 16 and an insulating jacket 18, may be mounted between two conducting electrodes 30 and 32 which are in turn connected in series, through a'switch 34, with a source of electrical power 36. closed, a strong flow of electrical current through the the copper sleeve 16 will produce heat by electrical resistance of the sleeve. The various circuit constants may be selected such that, with a momentary closing of the switch 34, the copper sleeve is heated sufficiently to fuse the surface of the nylon immediately adjacent thereto, and when the assembly is cooled this fused material When the switch 34 is produces a firm bond between the nylon jacket 18 and the copper sleeve 16. Where large cacapity condensers are available, a charge may'be built up in the condensers and discharged by short circuiting through the sleeve with just enough energy to give the desired shallow fusion.

Alternatively, as shown in Figure 6, the sleeve assembly 28 may be slid onto a heated mandrel 40, for example one that is heated by an internal resistance element, and then quickly removed. f The mandrel outer diameter should be such as to assure good heat transfer from the mandrel evenly to all of the copper sleeve 16. The mandrel may, for example, be provided with a slight taper to allow the sleeve assembly easily to be slid into position, and also to provide a means of stopping the sleeve when it has reached the proper position.

It has also been found that the fusion step may, in accordance with another aspect of the present invention, advantageously be performed by passing the sleeve assemblies one or more at a time axially through the magnetic field of an alternating current (advantageously high. frequency) induction coil, for example as pictured in Figure 7. As shown, the sleeve assembly 28 may be placed on an endless conveyor belt 46 which is supported in two places by two wheels 48 and 50, one of which is driven by a motor M so as to produce continuous and even motion of the conveyor belt in the direction of the arrow. The sleeve assembly 28 thereby will be drawn within the turns of the induction coil 52 which surrounds a part of the upper portion of the conveyor belt 46, and which is connected by two leads 54 and 56 to a source of A. C. power 58.

Alternatively, a high frequency induction heating coil may be positioned with its axis vertical, and the sleeve assemblies dropped therethrough. In either event, means should be provided for chilling the sleeves promptly after they have emerged from the induction heating coil, for example, as shown in Figure 7, by providing a tank of cold Water 60 in the drop path of the sleeves.

While the assembly 28 passes through the induction coil 52, part of the magnetic e'ld energy therein is convertedto heat in the copper sleeve by the resistivity of the copper. The intensity of the field and the duration of exposure to it (i. e. the speed of the conveyor belt 46) should be adjusted so that the total heat imparted to the copper sleeve is just sufficient to cause the nylon surface immediately adjacent thereto to reach its melting point without causing any fusion of the remainder of the insulation jacket. An exposure duration of from 2 to 4 seconds has been found to give quite satisfactory results with induction heating apparatus such as described hereinbelow. If the temperature ofthe metal gets too high, even though the duration of heating is short enough to get the desired thin fused film, the phenolic lacquer (if used) may become spongy and weaken the ultimate bond. If, on the other hand, the heating duration is too long, the nylon will fuse in too deep a layer and the insulation becomes brittle at very low temperatures so that it tends to shatter when the connector is crimped onto a conductor in arctic winter, or at less drastic temperatures in very dry atmosphere. Furthermore, it has been found that any time lag between removal of the sleeve assembly from the magnetic eld and entry into the cooling bath should ordinarily be not over about one second.

The induction heater unit used in this process was a commercially available model, having a power rating of 12.5 kilowatts at a frequency of 1.4 megacycles, and a 13 turn coil approximately three inches long with an inside diameter of about 1.25 inches.

After being chilled in the cold water bath, the sleeve assembly was then fitted step 5) over a connector barrel to provide a rigidly bonded, nylon-insulated connector (as shown in Figure l). It has been found that the bond created between the copper and the nylon, by means of the fusion bonding method described above, is

especially rugged and durable. Connectors having nylon sleeves formed thereon in accordance with the method just described when tested under many adverse conditions display important superiorities over other types of nylon-insulated connectors. For example, a connector having a nylon insulating jacket bonded in the manner above described can be successfully crimped at temperatures as low as 36 F., and after crimping can be taken to much lower temperatures in actual service without de terioration. The above-described method of insulating electrical connectors, although it has peculiar advantages with nylon, is also applicable to insulation materials other than nylon. For example, a rigid insulating jacket formed from an extruded rigid Vinyl plastic tube may be applied and bonded to the metal by this same process.

It has been found advantageous when using nylon for insulating purposes in accordance with the present invention, to soak the nylon jacket in water for a short while prior to fitting the jacket over the sleeve. This has been broadly disclosed and claimed by Harold Wooley in his U. S. patent application Serial No. 417,648, led March 22, 1954, now Patent No. 2,818,363, dated December 31, 1957. The soaking operation, which can readily be combined with a dyeing operation to impart a distinguishing color to the jacket, should be continued until a substantial amount of water has diffused into the nylon. The water in this case slightly plasticizes the nylon and thus minimizes the tendency of the nylon to crackiwhen it is pushed over the metal sleeve or when it is crirnpd.

It is important that the moisture in the nylon jacket be completely removed, or nearly so, prior to the fusion bonding step. For this purpose, it has been found desirable first to remove any water from the surfaces of the nylon jacket and sleeve, e. g., by centrifuging, and then evaporate the absorbed water from the nylon, e. g., by placing the assembly in an atmosphere of low humidity, and especially by exposing it to a stream of dry Warm air for at least 24 hours or until substantially all of the residual moisture has been removed.

This removal of moisture before the assembly is passed through the magnetic induction field not only avoids danger of blistering and resultant weakening of the nylon bond due to the effects of escaping moisture vapor released by the induced heat, but also causes the nylon jacket to shrink slightly and thus to grip the metal sleeve tightly in accordance with the invention of F. I. Sowa set forth and claimed in his U. S. patent application Serial No. 245,516, tiled October 1, 1951; and this substantially improves the adhesive bond.

In general, plasticizers for the plastic of the jacket may be used in this way instead of or in addition to the water and a small amount should be restored to or left in the plastic after the connector has been assembled and cemented, so that the jacket when crimped will be slightly l plasticized. For the nylon jacket specifically, water has been found most advantageous. To this end, the jacket and sleeve assembly may be soaked in water for a short period (e. g. two hours) after the fusion bonding to absorb moisture into the nylon. By retaining moisture in the nylon until the nal crimping operation, the quality of insulation and the resulting connection is substantially improved. To insure this moisture retention within the nylon insulation, the dampened connectors may be packaged in moisture-proof containers and removed only in lots sufficiently small to be used up before the absorbed moisture is lost.

It should be understood that the specific examples given hereinabove are illustrative of preferred embodiments and that other arrangements within the scope of the invention are feasible. For example, an adhesive bond between a nylon jacket and the metal ferrule may be obtained without using a cementing lacquer, it being possible merely to fuse a very thin layer of the nylon directly on the metal and it will adhere thereto. Also, it is apparent that a connector suitable for certain purposes may be provided without the seamless metal sleeve, by fusion-bonding nylon or plastic directly to the wire-receiving barrel of the connector. A secure and stable bond between the insulating jacket and the metal part of the connector is obtained by heat-induced fusion of non-metallic material. This bond is suiciently Strong to resist crushing and cracking and circumferential or axial displacement and consequent diminution of the insulation at the point of crimping, even though relatively large forces are applied for the compressive forging of the connector onto the conductor. Furthermore, the method of making such a connector provides manufacturing simplicities and efiiciencles not hitherto available in solderless connectors of this general type.

What is claimed is:

l. The method of bonding a deformable plastic sleeve to an inner conductive metal ferrule to form an assembly capable of being crimped to an electrical conductor, including the steps of (1) positioning a plastic sleeve over a bare metal ferrule in snug engagement therewith, (2) raising the temperature of the metal ferrule until the surface of the plastic sleeve in contact with the metal ferrule is caused to adhere to the metal ferrule, and then cooling the assembly, whereby the plastic sleeve becomes bonded to the metal ferrule.

2. The method set forth in claim 1, wherein a thin layer of adhesive resin cement is applied to the metal ferrule and dried thereon prior to assembling the insulating sleeve on the ferrule.

3. The method of claim 1 wherein the temperature of the ferrule is raised by introducing it into an alternating current induction field.

4. An electrical connector capable of being cold forged onto a conductor including a metallic ferrule capable of receiving a conductor, and a deformable plastic insulating sleeve engagingly surrounding the ferrule with that inner portion of the plastic sleeve immediately adjacent the ferrule having been fused by heat from the ferrule without causing any fusion of the remainder of the-plastic sleeve and thereby permanently bonded to the outside surface of the ferrule by adhesion of the plastic sleeve directly to the ferrule.

References Cited in the le of this patent UNITED STATES PATENTS 2,278,424 Campbell Apr. 7, 1942 2,288,918 Parker July 7, 1942 2,410,321 Watts Oct. 29, 1946 2,581,718 Schaffert Ian. 8, 1952 2,598,629 Whyte May 27, 1952 2,617,752 Von Hauteville Nov. 11, 1952 2,654,873 Sewengel Oct. 6, 1953 2,721,986 Badeau Oct. 25, 1955 OTHER REFERENCES Polyamide Resins by Hovey, page of Modern Plastics, May 1945. 

